This invention relates generally to a method of color reproduction and the apparatus employed therefor. More particularly, the invention concerns a method and apparatus employed in masking an original document so as to create color highlights or a color copy from a black and white or color original.
The process of electrophotographic printing is presently well-developed and generally employs an electrostatic latent image recorded on a photoconductive surface. Preferably, the electrostatic latent image is developed with heat settable toner particles. The toner powder image is transferred from the electrostatic latent image to a sheet of support material positioned closely adjacent thereto. Thereupon, the toner powder image is permanently affixed to the sheet of support material by the application of suitable heat thereto. Such a process is described in greater detail in U.S. Pat. No. 2,297,691 issued to Carlson in 1942.
Multi-color electrophotographic printing is substantially similar to black and white electrophotographic printing. However, rather than forming a total image of the original document, the light image is filtered producing a single color partial light image. This single color light image exposes the charged photoconductive surface to record a single color electrostatic latent image thereon. Suitable colored toner particles are then deposited on the single color electrostatic latent image to create a single color toner powder image. Thereafter, the single color toner powder image is transferred to the sheet of support material. This process is repeated a plurality of cycles with different colored light images and correspondingly colored toner particles. Each single color toner powder image is transferred to the sheet of support material in superimposed registration with the prior toner powder image. Thus, a composite multi-layered toner powder image is produced on the sheet of support material. This multi-layered toner powder image is then heated so as to be affixed permanently to the sheet of support material, thereby producing a color copy corresponding to the original document. Although the foregoing technique works satisfactorily for reproducing color copies from a color original no satisfactory approach has been developed for creating color copies from a black and white original. Frequently, only black and white originals are available and it is desired to produce a copy having highlighted areas in color thereon. Moreover, it may also be required to create a color copy from a black and white original. In addition, it is frequently necessary to mask portions of the original document so that they are not reproduced on the copy, or, in lieu thereof, to be capable of inserting various standard indicia onto copies which have been omitted from the original document. For example, it may be desirable to add a letterhead to a copy which was omitted from the original document.
Accordingly, it is the primary object of the present invention to improve the method and apparatus of electrophotographic printing so as to be capable of forming a copy having color highlights as well as inserting or deleting portions of an original document therefrom.